The objectives of this research are: 1) to examine the articulatory and phonatory characteristics of two groups of dysarthric speakers; 2) determine how those characteristics of speech motor control change during disease progression or as a result of pharmacological intervention: and 3) determine the acoustic features that are associated with changes in intelligibility. To achieve these objectives, three projects are proposed during the five year award period. In Project 1, which is a group comparison of ALS speakers with varying degrees of intelligibility, acoustic analyses of word and sentence production and phonatory analyses of steady state phonation will be completed in order to provide a needed data base regarding the nature of the dysarthria in ALS at different degrees of disease severity. Project 2, a series of within subject longitudinal studies, will examine the effects of disease progression in ALS on speech intelligibility through the use of perceptual, acoustic and physiological methods. Project 3 is designed to examine, through acoustic and phonatory analyses, the articulatory and phonatory characteristics of the dysarthria accompanying myasthenia gravis and the effects of two types of pharmacological intervention in this subject group.